third_party/WebKit/LayoutTests/webaudio/audiobuffersource-playbackrate-modulated-impulse.html

   1 <!DOCTYPE html>
   2 <html>
   3
   4 <head>
   5   <script src="../resources/js-test.js"></script>
   6   <script src="resources/compatibility.js"></script>
   7   <script src="resources/audio-testing.js"></script>
   8 </head>
   9
  10 <body>
  11   <script>
  12     description('AudioBufferSourceNode: DC-driven playbackRate modulation.');
  13     window.jsTestIsAsync = true;
  14
  15     var sampleRate = 44100;
  16
  17     // To get an observable change on playbackRate modulation, the minimum
  18     // rendering length should greater than the rendering quantum.
  19     var renderLength = 256;
  20     var half = renderLength / 2;
  21
  22     // With the playbackRate of 1, the duration of impulse buffer should be 4
  23     // samples (which means the interval between impulses is 4). Doubling
  24     // playback speed decrease the interval to 2 samples.
  25     var impulseLength = 4;
  26
  27     var context = new OfflineAudioContext(1, renderLength, sampleRate);
  28     var impulseBuffer, dcOffsetBuffer;
  29
  30     var audit = Audit.createTaskRunner();
  31
  32
  33     // Task: build an impulse and DC-offset buffers for testing.
  34     audit.defineTask('build-buffers', function (done) {
  35       // 4-sample impulse sample.
  36       impulseBuffer = createImpulseBuffer(context, impulseLength);
  37
  38       // Create a DC offset buffer with 2 values [0, 1] for modulating
  39       // playbackRate. The first half of buffer is 0 and the rest is 1.
  40       dcOffsetBuffer = context.createBuffer(1, renderLength, sampleRate);
  41       var dcOffsetArray = dcOffsetBuffer.getChannelData(0);
  42       for (i = 0; i < dcOffsetArray.length; i++) {
  43
  44         // Note that these values will be added to the playbackRate AudioParam
  45         // value. For example, 0 DC offset value will result playbackRate of 1
  46         // because the default playbackRate value is 1.
  47         dcOffsetArray[i] = i < half ? 0 : 1;
  48       }
  49
  50       done();
  51     });
  52
  53
  54     // Task: Render the actual buffer and compare with the reference.
  55     audit.defineTask('synthesize-verify', function (done) {
  56       var impulse = context.createBufferSource();
  57       var dcOffset = context.createBufferSource();
  58
  59       impulse.buffer = impulseBuffer;
  60       dcOffset.buffer = dcOffsetBuffer;
  61       impulse.loop = true;
  62
  63       impulse.connect(context.destination);
  64       dcOffset.connect(impulse.playbackRate);
  65
  66       impulse.start();
  67       dcOffset.start();
  68
  69       context.startRendering().then(function (renderedBuffer) {
  70         var data = renderedBuffer.getChannelData(0);
  71         var passed = true, i = 0;
  72         var nextImpulseIndex = 0;
  73
  74         while (i < renderLength) {
  75           if (i === nextImpulseIndex && data[i] === 1) {
  76             // From 0 to 127th element, the interval between impulses is 4. On the other
  77             // hand, the interval is 2 between 128th and 255th element.
  78             nextImpulseIndex += (i < half) ? impulseLength : impulseLength / 2;
  79           } else if (data[i] !== 0) {
  80             // If a value is neither 0 or 1, break the loop and fail the test.
  81             passed = false;
  82             break;
  83           }
  84
  85           i++;
  86         }
  87
  88         if (passed) {
  89           testPassed('Doubling playbackRate decreased the interval between impulses to half.');
  90         } else {
  91           testFailed('Doubling playbackRate produced the incorrect result' +
  92             'at the index ' + i + '.');
  93         }
  94       }).then(done);
  95     });
  96
  97     audit.defineTask('finish', function (done) {
  98       finishJSTest();
  99       done();
 100     });
 101
 102     audit.runTasks(
 103       'build-buffers',
 104       'synthesize-verify',
 105       'finish'
 106     );
 107
 108     successfullyParsed = true;
 109   </script>
 110 </body>
 111
 112 </html>